Ask HN: How do I work on startup ideas while working in industry?

Hello everyone, I am about to graduate from college in about a month. I very fortunately got a job waiting for me on the other side. But thanks to my dumb brain, I have decided to start developing a few of the ideas I've had simmering in my brain for a while. I am writing you today to ask, is there some sort of way to allow me to develop my ideas while also working the job and maintaining full control of the code I create for the ideas? I plan to use the money I make to build the idea. I have started repos on cloud servers, thinking that the timestamps would be like a "postmarked trademark" type of security. What else can I do to develop these ideas, maintain complete control of them, and still work in industry? EDIT: I have not started my job yet. I start shortly after graduation, but I have worked for the company before during the summer. Thanks and Cheers.